Topic: Strange Occurance

[rube2112]

I went out riding my cb750A the day before yesterday.  The planned ride was about 100 miles total.  I kept noticing that the headlight on high beam would dim and then brighten and then dim.  This did not happen on low beam.  Finall on the last 50 miles of the trip, the high beam blew out.  About 25 miles after that, my low beam blew.  None of the other lights on the bike have gone out and none of them get dim like the high beam did.  I will certainly be checking the voltage before I replace the bulb, but I was wondering if anyone had a gut feeling on this.  I'm leaning toward thinking it was a bad bulb that was damaged probably from vibration.  Any other ideas?  Thanks....Robb

[going4speed]

Sounds like loose connections to me.  A loose connection could cause the amperage across the bulb to exceed its allowance and blow out.

[rube2112]

Thats actually a real possibility too.....this is on a windjammer ss faring......that could be it.  I hate these kind of problems because they can be hard to pinpoint...Robb

[MoMo]

Loose connections is a real possibility,  I had a very similar problem-result was a loose plug. The bulb hadn't blown. Check the bulb with an ohmmeter, are you sure it is blown?

[Don R]

In 73 I had a brand spankin new cb500 do the same thing 2 times, then it never did it again. ?

[754]

 Might be internittent ground..

 Stock light is wire grounded thru stock harness, many custom changes are not.

 Athough the light is somewhat grounded thru the triple tree, there is grease on the bearings, at high rpm/vibration, it can become ungrounded..

 Dont ask how I found out, involves a buddy, bridge on a dark night, and light going out at 110 mph...

[rube2112]

I just checked the voltage at higher rpm's and it is 15.45.  The book says 14.5 at the batt at higher rpm's but I don't think this bike has the adjustable VR like the book says.  Any ideas?.....Robb

[rube2112]

Ok I did just adjust the voltage regulator and its right where its supposed to be.  I'm not sure how sensitive those bulbs are.  I hope this was the problem.  Robb

[Cuts Crooked]

  I'm leaning toward thinking it was a bad bulb that was damaged probably from vibration.  Any other ideas?  Thanks....Robb

I had the same thing happen several months ago. Replaced the bulb....no problems since then. So I think your vibration damage theory has merit.